The Torah in Parashat Behukotai (Vayikra 27:26) says about a Bechor (male firstborn kosher animal), “Lo Yakdish Oto” – that one may not consecrate it. This animal is considered consecrated as a Bechor from the moment of birth, and the Torah here forbids consecrating it as a different kind of sacrifice. Thus, it would be forbidden to declare the animal consecrated as an Ola sacrifice or a Shelamim sacrifice, since it is already consecrated as a Bechor. Tradition teaches that this verse establishes a general prohibition against declaring a change in the status of any consecrated animal. Once an animal has been consecrated as a particular sacrifice, one may not then consecrate it as a different sacrifice. Thus, for example, one may not declare a Shelamim consecrated as an Asham, or an Asham as a Hatat, and so on. Likewise, if one consecrated money for the maintenance of the Hechal (the interior of the Bet Ha’mikdash), he may not then declare the money consecrated for the maintenance of the altar. If a female animal was pregnant at the time it was consecrated, the fetus is also consecrated for the same purpose. Therefore, it is forbidden to change the status of the fetus by consecrating it for a different purpose, just like it is forbidden to change the mother’s status. The exception to this rule is a Bechor, which does not become consecrated until birth. While a firstborn animal is in its mother’s womb, it is not yet sacred. Therefore, if the owner, for whatever reason, wants to deny the Kohanim rights to Bechor (as the meat of the Bechor is eaten by the Kohanim), he can consecrate the Bechor as a different sacrifice – for example, an Ola – when it is still a fetus. The fetus becomes an Ola at that point, and thus does not become a Bechor at birth. This declaration is permissible, because it does not change the animal from the designation as one kind of sacrifice to the designation as a different sacrifice. This prohibition applies to both men and women, in all places, and at all times, even nowadays. Although one should not consecrate animals (or anything) else nowadays, in the absence of the Bet Ha’mikdash, nevertheless, if one did, the consecration takes effect. It then becomes forbidden to consecrate the animal as a different kind of sacrifice. One who consecrates a consecrated animal as a different sacrifice transgresses this prohibition, but he is not liable to Malkut, because this prohibition is transgressed without performing an action (“Lav She’en Bo Ma’aseh”).